User generated images of a geographic area are typically captured from a perspective at or near ground level. These ground based images can be a valuable resource for refining representations of a geographic area provided, for instance, by a geographic information system. For example, user generated images can be used to refine or generate high resolution three-dimensional models of various landmarks, buildings, objects, terrain, etc. in a geographic information system. For the user generated images to be useful, accurate camera parameters, such as the pose of the images, and/or geographic position of objects depicted in the image need to be determined. As used herein, the pose of an image refers to the position and orientation of a camera that captured the image relative to a reference.
Geographic information systems can include a database of aerial imagery of a geographic area. The aerial imagery can be captured from an aircraft and can provide an oblique perspective of the geographic area from one of various canonical viewpoints, such as north, south, east, and west canonical viewpoints. The database of aerial imagery can be associated with accurate pose information. The known pose information associated with the aerial imagery can be a valuable reference for determining camera parameters associated with ground based user generated images.
Various techniques for determining camera parameters associated with images are known, such as bundle adjustment techniques. For these techniques to provide good accuracy, features need to be reliably matched between sets of images. It can be difficult to identify reliably matched features between ground based images and aerial imagery due to the large differences in camera viewpoint and imaging conditions associated with the ground based images and aerial imagery.